Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – , India

Introduction Programmes and Courses  SEP–SBI082– CP01-03 SEP–SBI082–Unit01-03

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.3 Credits  Academic Inputs by Sonali Alkari Faculty YCMOU Nagpur Centre, Faculty LAD college P.G. D of Biotechnology Research officer Ankur Seeds Pvt Ltd

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.4 How to Use This Resource  Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling.  Discussion about students difficulties or tutorial with assignments should follow the lecture for about minutes.  Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.  Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.  Appear several times, for all the Self-Tests, available for this course.  Student can use handouts for last minutes preparation just before end exam.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.5 Learning Objectives  After studying this module, you should be able to:  Define operon  Explain diferent component of operon.  Explain Different types of operon requlation.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.6 Introduction: Operon  Operons are groups of genes that function to produce proteins needed by the cell.  Operons occur primarily in prokaryotes but also in some eukaryotes, including nematodes.  Although it may not be located in the operon gene, a "Regulator" gene is present which codes for the production of a repressor or corepressor protein.  The location and condition of the regulator, promoter, operator and structural DNA sequences can determine the effects of common mutations.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.7 Introduction: Operon  The first operon to be described was the lac-operon in Escherichia coli, by F. Jacob, D. Perrin, C. Sanchez and J.  Monod in the "Comptes rendus hebdomadaires des séances de l'Académie des sciences" in  Operons are related to regulons and stimulons.  Operons contain a set of genes regulated by the same operator, regulons contain a set of genes under regulation by a single regulatory protein, and stimulons contain a set of genes under regulation by a single cell stimulus.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.8 Operon An operon is a functioning unit of key nucleotide sequences including an operator, a common promoter, and one or more structural genes, which is controlled as a unit to produce messenger RNA (mRNA), in the process of protein transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.9 Operon  There are two different kinds of genes in operons:  Structural genes code for proteins needed for the normal operation of the cell.  For example, they may be proteins needed for the breakdown of sugars.  The structural genes are grouped together and a single mRNA molecule is produced during their transcription.  Regulator genes code for proteins that regulate other genes.  Operons have not been found in eukaryotes

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.10 Operon as a Unit of Transcription:1  An operon contains one or more structural genes which are transcribed into one polycistronic mRNA: a single mRNA molecule that codes for more than one protein. s  Upstream of the structural genes lies a promoter sequence which provides a site for RNA polymerase to bind and initiate transcription. Close to the promoter lies a section of DNA called an operator.  The operon may also contain regulatory genes such as a repressor gene which codes for a regulatory protein that binds to the operator and inhibits transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.11 Operon as a Unit of Transcription:2  Regulatory genes need not be part of the operon itself, but may be located elsewhere in the genome.  The repressor molecule will reach the operator to block the transcription of the structural genes.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.12 Operator  An operator is a segment of DNA which regulates the activity of the structural genes of the operon that it is linked to, by interacting with a specific repressor or activator.  It is a regulatory sequence for shutting a gene down or turning it "on".

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.13 Promoter  A promoter is a DNA sequence that enables a gene to be transcribed.  The promoter is recognized by RNA polymerase, which then initiates transcription.  In RNA synthesis, promoters indicate which genes should be used for messenger RNA creation - and, by extension, control which proteins the cell manufactures.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.14 Operon Gene Regulation  Control of operon genes is a type of gene regulation that enables organisms to regulate the expression of various genes depending on environmental conditions.  Operon regulation can be: positive. negative  Negative regulation involves the binding of a repressor to the operator to prevent transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.15 Negative Inducible Operons :1  In negative inducible operons, a regulatory repressor protein is normally bound to the operator and it prevents the transcription of the genes on the operon.  If an inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator.  This allows for the transcription of the genes on the operator.  In negative repressible operons, transcription of the genes on the operon normally takes place.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.16 Negative Inducible Operons:2  Repressor proteins are produced by a regulator gene but they are unable to bind to the operator in their normal conformation.  However certain molecules called corepressors can bind to the repressor protein and change its conformation so that it can bind to the operator.  The activated repressor protein binds to the operator and prevents transcription

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.17 Positive Inducible Operons  In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA.  However, certain substrate molecules can bind to the activator proteins and change their conformations so that they can bind to the DNA and enable transcription to take place.  In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment.  However, certain molecules can bind to the activator and prevent it from binding to DNA. This prevents transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.18 Negative and Positive Control:1  The trp and lac operons discussed above are examples of negative control because a repressor blocks transcription.  In one case (lac operon) the repressor is active and prevents transcription.  In the other case (trp) the repressor is inactive and must be activated to prevent transcription.  Positive control mechanisms require the presence of an activator protein before RNA polymerase will attach.  The activator protein itself must be bound to an inducer molecule before it attaches to mRNA

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.19 Negative and Positive Control:2 Structural Genes Repressor or Regulator Negative Control (an active repressor inhibits transcription) Inducible Operons InactiveActive (inhibits) Repressible Operons ActiveInactive (inhibits when activated) Positive Control (an active regultor promotes transcription InactiveInactive (promotes when activated)

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.20 Negative and Positive Control:3 Genes which code for enzymes necessary for the digestion of maltose are regulated by this mechanism. Maltose acts as the inducer, binding to an activator and then to mRNA. The activator bound to mRNA stimulates the binding of RNA polymerase.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.21 What You Learn…  Operons are groups of genes related to regulons and stimulons  Structural genes code for proteins.  Regulator genes code for proteins that regulate other genes.  An operator is a segment of DNA which regulates the activity of the structural genes of the operon.  A promoter is a DNA sequence that enables a gene to be transcribed.  In negative repressible operons, transcription of the genes on the operon normally takes place.  Where as in positive inducible operons, certain molecules can bind to the activator and prevents transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.22 Critical Thinking Questions 1.Write in details about operon. 2.State different kinds of genes in operons. 3.Decribe in details about Operon regulation and different types of operon regulation with.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.23 Hints For Critical Thinking Question 1.Write as short note on operon and its role and importance transcription. 2.State in details about Structural genes and Regulator genes. 3.State in detail What is Operon regulation different types as positive, negative and positive and negative. © 2007, YCMOU. All Rights Reserved.23

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.24 Study Tips:1  Book1 Title: Genes IX. Author: Benjamin Lewin Publisher: Jones & Bartlett Publishers  Book2 Title: Genetics from Genes to Genomes Author: L. H. Hartwell, L. Hood, M. L. Goldberg Publisher: Tata McGraw-Hill

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.25 Study Tips:2  Book3 Title: Genetics Author: Monore W.Strickberger Publisher: Prentice Hall of India  Book4 Title: Genetics Author:C.Serin Publisher: Tata McGraw-Hill

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.26 Study Tips Microsoft Encarta Encyclopedia Wikipedia the free encyclopedia

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